St-Pierre undergoes knee surgery

Former UFC champion Georges St-Pierre has undergone knee surgery, but has yet to say when he will return.

The mixed martial arts star from Montreal tore the anterior cruciate ligament in his left knee during training.

He tweeted a photo of himself in shorts, t-shirt and leg brace on a hospital gurney. He calls the surgery a success and said on Wednesday night: "Road to Recovery has started again."

St-Pierre (25-2) vacated his 170-pound title in December, saying he needed a break from the sport. But he kept training and hurt his knee during a workout. The 32-year-old fighter had reconstructive surgery on his other knee in December 2011.